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Job 38:4-7 “Where were you when I laid the foundations of the earth? ... When the morning stars sang together, And all the sons of God shouted for joy?"

"Morning stars" and "sons of God" appear to be references to angels. (One could debate this, of course.) If they sang and shouted when the Earth was created, and according to Genesis 1 the Earth was created before humans, then the angels must have been created before humans.

Satan tempted Adam and Eve in Genesis 3, and as you mention there's the reference to an angel standing guard at Eden. So if angels were created after humans, it was not long after. Not more than one generation, anyway.

Christians generally interpret the "let us ..." statements of Genesis 1 as the persons of the Godhead speaking to each other, i.e. Father, Son, and Holy Spirit conversing among themselves. There's no indication of angels participating in creation or of humans being created in the image of angels, but both Father and Son are described as creating, so this generally makes more sense than supposing that the "we" means God and angels. (I'm not sure how Jews interpret this.)

If in Genesis 1:26,God was talking to the angels when he said, "Let us make man in our image, after our likeness," then God was acknowledging the angels as his equal, a concept that has no biblical or scholarly support. On the other hand, Mark S. Smith says, in The Early History of God, page 64, that on the available evidence, Israelite religion in its earliest form was polytheistic and the number of deities was relatively typical for the region. It is therefore more meaningful for these words to reflect an earlier belief, with God (YHWH) talking to his fellow gods about creation.

Cherubim, such as those who guarded the entrance to the Garden of Eden (Genesis 3:24), existed in many ancient Near Eastern cultures and were mythical creatures with the head of a bull, the wings of an eagle, the feet of a lion, and the tail of a serpent, so therefore not angels as we would understand them. We can not say from their sudden appearance in Genesis 3:24 whether they were created before man or newly created to guard the entrance to the Garden. Angels ('messengers'), as we know them, were not mentioned in any scripture written before the Babylonian Exile.